1. Field of the Invention
This invention relates to a signal processing scheme utilizing an oversampled switched capacitor filter.
2. Description of the Related Art
Transmitters such as wireless baseband transmitters must convert digital codes from a digital modulator to analog voltages. Conventional signal processing schemes employed for this purpose comprise a digital-to-analog converter (DAC), a switched capacitor filter (SCF) to suppress spurious signals that would interfere with adjacent channels, and an RC active filter (RCF) to further reduce such interference and reject signal images at the operating frequency of the SCF and its multiples. The RCF in these conventional schemes is typically a fourth or higher order filter requiring many high precision capacitors and resistors.
To create these components, implementation of the RCF of the conventional scheme requires use of enhanced analog chip fabrication processes. Such processes require several extra masks, which entail higher production costs and increased development time. By contrast, digital chip fabrication processes are cheaper and can be developed faster, but do not provide high precision capacitors and resistors. These components must be provided off-chip, requiring connections to I/O pads with high parasitic capacitance. Productions costs increase as more high precision off-chip components are required.
Therefore, an object of this invention is to provide a signal processing scheme for digital to analog conversion which is suitable for implementation by digital processes and requires a minimum number of off-chip components.